Need desoldering advice

I was working on a lathe with a Fanuc 0-TC control today that could not download programs and I suspect the 751488 line driver. Disabling Xon/Xoff let us load a program. I ohmed the db25 connector to M5 on the memory board. The wires are good. One of those led things you plug in shows no activity on Tx coming out of control. Iow, it hears fine, but is mute.
I have a new memory board on the way but would love to replace the chip and have a spare for the other machine of this type. I remember seeing a tip that was the outline of a 14 pin dip years ago but I can't find it now.
What is the current best practice for desoldering 14 - 16 pin DIP packages? What is the lesser expensive options? ;)
Thanks,
Wes

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Just cut all of the pins firs (close to the chip) and then holding the pins with your cutters unsolder them while pulling. After they are all out, use a desoldering tool (solder sucker) Daveb

snipped-for-privacy@nt.org (DaveB) wrote:
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As was suggested cut the leads close to the IC. Now, provided you have enough clearance above the board, straighten the cut off pins vertically. Then using a fine point soldering iron solder an IC socket pin by pin to those on the board. This way there is less chance of damaging the board traces.
Chuck P.

If you have never don't this before, here are a few tips.....
First off, its really easy to de-laminate the copper traces and pads from the fiberglass board, with to much heat!!! don't use that big old 100/300 watt soldering iron!! use a 15 watt cheapo from radio shack. Don't work on each pin in a row, alternate pins or give the board a little time to cool, between operations....Its not hard, just use common sense.
First before you even start, mark the board where the "U" shaped notch on the chip is. If you don't you might forget which way the chip goes on the board.
Next cut all the chip legs, as close to the chip as you can. The left over bits of the legs on the board will become handles when you take desolder them. I would suggest maybe getting one of these (http://www.radioshack.com/product/index.jsp?productId 62731&cp=&sr=1&origkwÞsolder&kwÞsolder&parentPage=search to desolder with. You can hook it up to a normal light dimmer and cut the wattage way back, because the one listed is 45 watts, a little to big for my tastes. What your trying to do here is remove the cut off legs and open up the through hole on the board with heat and suction. Once all the holes are open, you can install a chip socket, then its really easy to replace the chip the next time it cooks.... Just go slow and keep cool (pun intended!!!)
here is a great site, yes I know its about pinball machines, but it does have a great section on desoldering and soldering both...
http://www.pinrepair.com/begin/index.htm#desolder
also on the same page look at section 3.f how to use it:soldering a circuit board...
Hope that helps...
Bob in phx (who has burnt up his fair share of circuit boards, both with a soldering iron and electricity too!!!)
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I would STRONGLY recommend against a socket - in general experience has shown that the sockets are less reliable than the chips - if you expect to be changing it a lot, a socket is good, otherwise, eschew it

William, I would respectfully like to disagree. Machine pinned sockets are very reliable. I have never worked on the control boards for this machine, but I have had years of pinball machine repair and have never once had a machine pinned socket fail. Pinball machines live in a very hostile environment, with vibrations, liquids, smoke and all other sorts of mechanical and electrical stresses. The dual wiper sockets (scanbe brand) are indeed bad, but not the machined ones...just my opinion, no disrespect intended.
bob in phx.
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My first job out of tech school was repairing pinball machines for an amusement operator. I second the socket idea. Less of a chance for a newbie to fry the IC. I've installed plenty of them. I've never had a problem with socket failure.
Folks seem to like the solder suckers, but I like the chem-wick braid. It's easier to pack in the tool bag.
Bob in Phx wrote:
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Wes,
Wow - a popular topic tonight. I suggest a couple of things that I didn't see mentioned: 1) BACKUP the machine if you don't have a very good parameter list. (Naturally, you'll have to do this by hand since the port is blown).Things that get changed on the factory list include RS-232 parameters and backlash values. Fanuc 0C's have a supercap on the memory board that should hold the parameters while the board is unplugged. Sometimes the board gets laid on metal and the supercap drains. 2) Also, find out what blew the port. Mostly, they get blown because of bad / broken ground wiring on the PC side. Also, if the PC is plugged into an area of the building different from the electrical system running the machine tool AND the grounding is poor, high voltages flow down the RS-232 wiring.
Warren Uptime Electronics, Inc.

On Thu, 12 Jun 2008 21:40:22 -0700, "William Noble"
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Use machined pin sockets and the reliability goes WAY up - and no chance of overheating the chip soldering it in.

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    That depends on several things.
1)    Quality of socket. (A socket with machined pins grips better     than any of the sockets with pins bent up from flat metal, and     some of the bent ones grip better than others.)
2)    Number of pins. The more pins, the better the grip of the     socket on the chip.
3)    The amount of vibration to which the board is subjected. If     there is a lot of vibration, there is a greater chance of the     chip walking out of the socket. Examples of poor places to use     sockets would include control logic boards for CNC machines,     automotive boards (especially racecar boards), and pinball     machines with real pinballs and flippers. The ones which are     purely logic and displays are a different matter, as long as the     users don't keep trying to "tilt" them anyway. :-)
4)    The mass of the chip. An example would be the old TRW 16x16     bit multiply chip with an integral heat sink -- this would be     more likely to walk out of a socket than say a Motorola MC68000     CPU chip, which does not have the extra mass of the heatsink.
    I forget what the board came from -- if it was even mentioned at the beginning of the thread.
    I would probably make a tradeoff decision based on how likely subsequent failures of the chip were compared to the amount of vibration to which it would be subjected. It is possible to include clamp-down hardware to overcome the vibration walk-out problem.
    Another factor would be the cost to replace the board -- because having to unsolder and replace chips multiple times in a single location on a board increases the chances of damaging the board -- and lacking a diagram showing which pins connect to where (thus allowing external jumpers to replace a failed internal trace -- if the speed is not too high for this to be practical) would tilt my choices towards the socket.
    Enjoy,         DoN.

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Ive found that a tiny drop of Super Glue on an opposed set of leads tends to keep chips from walking, and is easily removed with a touch from a soldering pencil
gunner

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    Hmm ... an interesting idea. Thanks.
    Enjoy,         DoN.

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I was desperate to keep MC-2 card socketed chips in their nests on Omniturns running bar feeders with no liners.
Been working pretty good now for about 8 yrs since I first tried it.
Gunner

On Sat, 14 Jun 2008 23:30:10 -0700, Gunner Asch
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I've used RTV style silicone, hot glue (just a dab) and the way some sockets area made you can slip a small wire tie through underneath.
The bigger problem I've had with sockets is just poor connections that occur over time. Equipment develops a strange intermittent problem. Pull/rock the chip in its socket (chip was still fully seated) and the problem goes away for awhile. Those problems where always a lot of fun to troubleshoot/fix :(

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That is a excellent link for more than just desoldering.
Thanks,
Wes

Yep, the entire site is well written, well organized and well loved by the pinball community. I enjoy fixing them up as it really takes knowledge in all sorts of fields. From paint to engineering to mechanics to electrical, to circuit board logic... And the kids like to play them!!!!!!!!!!
bob in phx
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download programs
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program. I ohmed
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those led
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hears fine, but
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and have a spare
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outline of a 14
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packages? What is the
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Firts clip it loose and then suck / blow out the solder using a bulb type desolder device, lastly heat again and one by one pick out the remaining leads using a roachclip or fine tweezer.
Be really careful its actually pretty easy to mess up a multi layer board if you go into it halfhazardly heating / pulling on the old component IOW dont try and play dentist removing teeth here.

Wes wrote:
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For desoldering, the integrated solder sucker soldering iron that has the spring loaded plunger type vacuum pump will do the job. A real desoldering station is of course better. Solder wick is a last resort.
The all-at-once type tips aren't great since they leave the solder clogging the device holes in the PCB. Think of them more for salvaging useable parts, than for rework.
Be glad you aren't trying to rework a surface mount board, they can be a real pain in the posterior without special tools.

"Pete C." wrote:
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Bullshit! SMD devices are much easier to rework than through hole. I have removed & replaced 288 pin MPU chips with solder wick, a couple drops of Kester 1544 RMA liquid rosin flux, and an common Edsyn Loner soldering iron. The chip was installed 90 degrees off, so I removed most of the solder from the leads, then used a small curved pick and the edge of the soldering iron's tip to heat each pin, near the body. When it was hot enough it would pop loose from the pad. By the time you removed the iron and pick, it had cooled, so I moved to the next pin. All it takes is good eyesight, and steady hands. Soldering it back was even faster. A drop of the flux down each side, and tack opposite corners, then run a drop of solder down each row. Any excess was still on the tip when each row was finished. For bad SMD resistors and capacitors, a pair of irons made quick work of removal, and replacement. You work fast, to eliminate heat damage, and a pair of irons makes the surface tension properly center the new part on the pads.
The only 'Special tool'' I used was a stereo microscope, since my vision is so poor. I would have needed it for a lot of through hole rework, as well.

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The advice to clip the pins is really the safest way to remove the chip. A Dremel cutoff wheel works pretty good as does a very fine pointed pair of cutters. There are desoldering tips made to heat all pins at once and there are also spring loaded clips to pop the chip off when the pins are free. There are also hot-air desoldering systems but all of these things work better with experience.
If possible, my advice would be to have someone experienced do this while you watch, if you want to be sure not to damage the board. It's not difficult but it is easy to make a mistake.
Don Young